Because palladium catalysts are important in carbon-carbon (hetero element) bond-forming reactions, palladium nanoparticle (PdNp) catalysts and reactions employing them have been reported over the past decade (for example, Nonpatent Reference 1). In PdNp catalysts, the surface area of the nanoparticles (Np) is broader and more active than in bulk catalysts. As a result, they are characterized as reactions that progress under mild and environmentally-friendly conditions. For example, it has recently been progressively found that traditional reactions that progress using 0 valence/divalent palladium catalysts in the presence of ligands, including phosphine ligands and nitrogen-containing heterocyclic carbene (NHC), can progress ligand free when employing PdNp. Thus, there are numerous advantages, not just in terms of cost, but also in terms of post-processing and product purification. Particularly in the areas of pharmaceutical and functional molecule synthesis, it is thought that their importance will continue to increase beyond what it is today.
The method of manufacturing the above metal Np utilizes polymers and ionic liquids (Nonpatent Reference 1).
The present inventors have successfully developed sulfur-modified Au-supported Pd catalysts (SAPd). When employing an SAPd, by repeatedly conducting (several hundred to several thousand times) ligand-free Pd cross-coupling (Suzuki-Miyaura coupling, a carbon-carbon bond-forming reaction, and the Buchwald-Hartwig reaction, a carbon-nitrogen bond-forming reaction), the quantity of Pd leakage in the reaction solution is on the order of 10 to 100 ppb (Nonpatent References 2 and 3, Patent Reference 1). This is the first example of an SAPd that permits a ligand free Buchwald-Hartwig reaction.    [Patent Reference 1] WO2011/010610 and US2012/0115714    [Nonpatent Document 1] A. Balanta, C. Godard and C. Claver, Chem. Soc. Rev. 2011, 40, 4973.    [Nonpatent Document 2] J. Am. Chem. Soc. 2010, 132, 7270-7272.    [Nonpatent Document 3] Adv. Synth. Catal. 2011, 353, 743-748.